The disclosure of Japanese Patent Application No. 2000-237456 filed on Aug. 4, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to a brake control apparatus and a brake control method for a vehicle wherein braking forces are applied to wheels automatically by controlling a pressure of operating fluid in addition to braking operation by a driver.
2. Description of Related Art
As disclosed in Japanese Patent Application Laid-Open No. 11-321619, a brake control apparatus applies braking forces automatically under a predetermined condition in addition to a braking operation by a driver. Such a brake control apparatus is usually provided with a fluid pressure actuator capable of controlling a pressure of operating fluid supplied to wheel cylinders in addition to the braking operation by a driver. By performing operation control of the fluid pressure actuator, desired braking forces are generated. Such a fluid pressure actuator is for example composed of a pump that force-feeds operating fluid and a control valve that switches over oil passages or controls a flow rate of the operating fluid.
In this manner, the fluid pressure actuator controls braking forces automatically using the pump for force-feeding operating fluid as a fluid pressure source. In the case where a malfunction occurs, in the fluid pressure actuator including the pump and the control valve, a time period of ten seconds to 100 seconds is required to electrically detect the malfunction. Meanwhile, the pressure of the operating fluid supplied to the wheel cylinders may rise unnecessarily.
To solve such a problem, the invention provides a vehicular brake control apparatus capable of preventing an unnecessary rise in the pressure of the operating fluid supplied to the wheel cylinders where a malfunction occurs in a fluid pressure actuator during automatic control of the braking forces.
A vehicular brake control apparatus according to a first aspect of the invention comprises brakes that apply braking forces corresponding to a pressure of supplied operating fluid to wheels, a pump that force-feeds operating fluid, a valve that adjusts a pressure of operating fluid force-fed from the pump, and a controller. The controller performs operation control of the pump and the valve and controls a pressure of the operating fluid to be supplied to the brakes. The controller also controls a pressure-increasing gradient of the fluid pressure by controlling both the pump and the valve during pressure-increasing control for increasing the fluid pressure in the brakes.
Thus, even if a malfunction occurs in one of the pump and the valve, the other functions normally. Therefore, an unnecessary rise in the fluid pressure in the brakes can be prevented.
Further, the valve may be connected to a suction port of the pump to control an opening state of communication of an operating fluid passage.
The amount of flow of operating fluid sucked by the pump via the operating fluid passage as a circulating passage is controlled by the valve. Thus, even in the case where a malfunction that could lead to an increase in discharge amount occurs in the pump, since the suction amount is limited, an increase in discharge amount can be prevented. Further, even if the control valves have been closed completely due to a malfunction, since the pump is drivingly controlled normally, an unnecessary rise in the fluid pressure in the brakes can be prevented.
Further, during pressure-increasing control, the pump may be duty-driven, and the opening and closing of the valve may also be duty-driven.
A vehicular brake control apparatus according to a second aspect of the invention comprises a master cylinder that changes a pressure of operating fluid in accordance with a brake operating force, brakes that apply braking forces corresponding to a pressure of operating fluid supplied from the master cylinder to the wheels, a pump that force-feeds operating fluid, control valves that are provided in communication passages between the master cylinder and the brakes and that control an opening state of the communication passage. An introduction passage is provided for introducing operating fluid that has been force-fed from the pump to the communication passages between the control valves and the brakes, and a controller performs operation control of the pump and the control valves and controls a pressure of operating fluid to be supplied to the brakes. The controller closes the control valves and stops operation of the pump during pressure-holding control for holding fluid pressure in the brakes.
According to the second aspect, during pressure-holding control (constant-pressure control) for holding fluid pressure in the brakes, the control valves are closed, whereby the communication passages between the master cylinder and the brakes are shut off. The operating fluid that has been delivered from the pump is encapsulated between the pump and the brakes. A stopped state of the pump is maintained during pressure-holding control. Thus, in comparison with the case where fluid pressure paths are switched over with the pump being driven so that the fluid pressure applied to the brakes is held, an unnecessary rise in the fluid pressure in the brakes can be reliably prevented because the pump is out of operation during pressure-holding control.
Further, a vehicular brake control apparatus according to a third aspect of the invention comprises a master cylinder that changes a pressure of operating fluid in accordance with a brake operating force, brakes that apply braking forces corresponding to a pressure of operating fluid supplied from the master cylinder to wheels, a pump that force-feeds operating fluid, control valves are provided in communication passages between the master cylinder and the brakes and control an opening state of the communication passages. An introduction passage is disposed for introducing operating fluid that has been force-fed from the pump into the communication passages between the control valves and the brakes, and a controller performs operation control of the pump and the control valves and controls a pressure of operating fluid to be supplied to the brakes. The controller opens the control valves and stops operation of the pump during pressure-reducing control for reducing fluid pressures in the brakes.
According to the third aspect, the control valves are opened during pressure-reducing control for reducing fluid pressure in the brakes, whereby the operating fluid encapsulated between the pump and the brakes flows toward the master cylinder. While the control valves are open, a stopped state of the pump is maintained. Thus, in comparison with the case where fluid pressure applied to the brakes is reduced by performing operation control of the pump, an unnecessary rise in fluid pressure in the brakes can be reliably prevented because the pump is out of operation.
The aspects of the invention should not be limited to the vehicular brake control apparatuses as described above. For example, other aspects of the invention include a vehicle equipped with a vehicular brake control apparatus and a method of controlling a vehicular brake control apparatus.